ASoC sst v2: Add medfield machine driver

This patch adds the medfield machine driver
Machine driver glues the sn95031 codec driver and sst_platform driver to form the asoc sound driver

Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Harsha Priya <priya.harsha@intel.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>